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Results for “Integrin alphaVbeta3”

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PubMed2000

Adherence to osteopontin via alphavbeta3 suppresses phorbol ester-mediated apoptosis in MCF-7 breast cancer cells that overexpress protein kinase C-alpha.

Overexpression of protein kinase C-alpha in MCF-7 breast cancer cells (MCF-7-PKC-alpha cells) results in anchorage-independent growth and increased tumorigenicity of these cells in nude mice. MCF-7-PKC-alpha cells, unlike their parental MCF-7 cells, are sensitized to apoptosis by phorbol esters. When adhered to osteopontin, a bone matrix protein, MCF-7-PKC-alpha cells were resistant to phorbol ester mediated apoptosis. Fluorescence-activated cell sorting revealed that osteopontin receptors, alphavbeta3 and alphavbeta5, are expressed on MCF-7-PKC-alpha cells and that both are used to adhere to osteopontin. Addition of an RGD-containing peptide inhibited survival of MCF-7-PKC-alpha cells exposed to phorbol ester and adhered to osteopontin. This indicated that an integrin was involved in the cell death suppression signal. Whereas, anti-alphavbeta5 antibody did not reduce survival of MCF-7-PKC-alpha cells adhered to osteopontin, anti-alphavbeta3 antibody could efficiently block suppression of apoptosis. Phorbol ester also induced increased expression of alphavbeta3 on MCF-7-PKC-alpha cells by upregulating expression of a second species of beta3 mRNA. This study suggests that breast cancer cells that have metastasized to bone may have a survival advantage resulting from interaction of alphavbeta3 on these cells with the bone protein osteopontin.

Adenocarcinoma↗

PubMed1997

Cloning and characterization of a novel integrin beta3 subunit.

We have identified a novel integrin beta3 subunit, termed beta3C, from a human osteoclast cDNA library. The COOH-terminal sequence and 3'-untranslated region of the beta3C subunit differs from the previously reported beta3A (platelet) and beta3B (placenta) sequences, while the regions coding for the transmembrane and extracellular domains are identical. The beta3C cytoplasmic domain contains 37 amino acids, the last 17 of which are encoded by a novel exon located about 6 kilobase pairs downstream of exon 14 of the beta3A gene. HEK 293 cells were stably co-transfected with alphaV and either beta3C (HEKbeta3C) or beta3A (HEKbeta3A). The viability of HEKbeta3C cells was lower than that of HEKbeta3A cells, and HEKbeta3C cells in culture grew as clusters rather than as a monolayer. The novel cytoplasmic domain did not affect receptor binding affinity; both alphaVbeta3A and alphaVbeta3C isoforms exhibited high affinity binding to 125I-echistatin and cyclic and linear RGD peptides. However, in contrast to HEKbeta3A, HEKbeta3C cells failed to adhere to osteopontin, an alphaVbeta3 matrix protein. The data provide further support for the key role of the cytoplasmic domain of the beta3 integrin in cell adhesion and suggest a potential role for the beta3C integrin subunit in modulating cell-matrix interactions.

Amino Acid Sequence↗

PubMed1997

Fibrinogen is a ligand for integrin alpha5beta1 on endothelial cells.

Previous studies have shown that fibrinogen can associate with endothelial cells via an Arg-Gly-Asp (RGD) recognition specificity. In the present study, we have characterized the specificity of fibrinogen binding to endothelial cells under different cation conditions. Fibrinogen binding to suspended endothelial cells was selectively supported by Mn2+ and was suppressed by Ca2+. The Mn2+-supported interaction was completely inhibited by RGD peptides but not by alphavbeta3 blocking monoclonal antibodies. In contrast, the interaction was completely blocked by two alpha5beta1 monoclonal antibodies. This interaction was not mediated by fibronectin bound to the integrin; could be demonstrated with purified alpha5beta1; and also was observed with a second alpha5beta1-bearing cell type, platelets. The binding of fibrinogen to alpha5beta1 on endothelial cells in the presence of Mn2+ was time-dependent, specific, saturable, and of high affinity (Kd = 65 nM). By employing anti-peptide monoclonal antibodies, the carboxyl-terminal RGD sequence at Aalpha 572-574 was implicated in fibrinogen recognition by alpha5beta1. Two circumstances were identified in which alpha5beta1 interacted with fibrinogen in the presence of Ca2+: when the receptor was activated with monoclonal antibody (8A2) or when the fibrinogen was presented as an immobilized substratum. These results identify fibrinogen as a ligand for alpha5beta1 on endothelial and other cells, an interaction which may have broad biological implications.

Cells, Cultured↗

PubMed1999

Role of hypoxia and extracellular matrix-integrin binding in the modulation of angiogenic growth factors secretion by retinal pigmented epithelial cells.

The retinal pigmented epithelium (RPE) is a monolayer of polarized cells located between retinal photoreceptors and blood vessels of the choroid. The basal surface of RPE cells rests on Bruch's membrane, a complex extracellular matrix structure which becomes abnormal in several disease processes, including age-related macular degeneration (AMD). Ruptures or abnormalities in Bruch's membrane are frequently accompanied by choroidal neovascularization. Disturbed interaction of RPE cells with their extracellular matrix (ECM) could play a role in this process. The present study was undertaken to examine the complex interactions between hypoxia, integrin, and ECM in the regulation of RPE functions. Antibody blocking experiments demonstrated that RPE cell adhesion to vitronectin is mediated primarily through alphavbeta5 and adhesion to fibronectin occurs through alpha5beta1. RPE adhesion to immobilized laminin demonstrated highest level of non-RGD-mediated adhesion as compared to that with collagen IV or the RGD matrices such as vitronectin (alphavalpha5) , fibronectin (alpha5beta1), or thrombospondin (alpha5beta1 + alphavbeta5). Addition of soluble vitronectin, or fibrinogen to RPE cell cultures resulted in a small to moderate increase in VEGF and FGF2 in the media, while each of these growth factors was dramatically increased after addition of thrombospondin 1 (TSP1). In contrast, soluble fibronectin resulted in differential upregulation of VEGF but not FGF2. Similarly, immobilized TSP1 resulted in differential greater upregulation in VEGF but not FGF2 release from RPE as compared to other ECMs under either normoxic or hypoxic conditions. Additionally, hypoxia resulted in a time-dependent increase in VEGF, but not FGF2 release in the media. RPE cells grown on TSP1-coated plates showed increased VEGF and FGF2 in their media compared to cells grown on plates coated with type IV collagen, laminin, vitronectin, or fibronectin. The TSP1-induced increase in secretion of growth factors was partially blocked by anti-alpha5beta1, anti-alphavbeta3, and anti-alphavbeta5 antibodies indicating that it may be mediated in part by TSP1 binding to those integrins. These data suggest that alterations in oxygen levels (hypoxia/ischemia) and ECM of RPE cells, a prominent feature of AMD, can cause increased secretion of angiogenic growth factors that might contribute to the development of choroidal neovascularization. These data also suggest the potential modulatory role of VEGF release from RPE by ECM and alphavbeta5 and alpha5beta1 integrins.

Antibodies, Monoclonal↗

PubMed1997

Identification of a region in the integrin beta3 subunit that confers ligand binding specificity.

Many integrin adhesion receptors bind ligands containing the Arg-Gly-Asp (RGD) peptide motif. Most integrins exhibit considerable specificity for particular ligands and can distinguish among the many conformations of RGD. In this study we identify the domain of the integrin beta subunit involved in determining ligand binding specificity. Chimeras of beta3 and beta5, the most homologous integrin beta subunits, were expressed with alphav on the surface of human 293 cells. The ligand binding phenotype of each chimera was assessed using the ligands Fab-9 and fibrinogen, both of which have a binding preference for alphavbeta3. The results of the study show that when exons C and D of the beta3 subunit (residues 95-233) are substituted into beta5, the chimera gained the ability to bind Fab-9 with an affinity close to that of wild-type alphavbeta3. This chimera was able to mediate cell adhesion to fibrinogen. Furthermore, the swap of only a 39-residue segment of this larger domain, beta3 residues 164-202, into the backbone of beta5 enabled the chimeric integrin to bind soluble Fab-9. This small domain is highly divergent among the integrin beta subunits, suggesting that it may play a role in determining ligand selection by all integrins.

Amino Acid Sequence↗

PubMed2003

Structure of integrin alpha5beta1 in complex with fibronectin.

The membrane-distal headpiece of integrins has evolved to specifically bind large extracellular protein ligands, but the molecular architecture of the resulting complexes has not been determined. We used molecular electron microscopy to determine the three-dimensional structure of the ligand-binding headpiece of integrin alpha5beta1 complexed with fragments of its physiological ligand fibronectin. The density map for the unliganded alpha5beta1 headpiece shows a 'closed' conformation similar to that seen in the alphaVbeta3 crystal structure. By contrast, binding to fibronectin induces an 'open' conformation with a dramatic, approximately 80 degrees change in the angle of the hybrid domain of the beta subunit relative to its I-like domain. The fibronectin fragment binds to the interface between the beta-propeller and I-like domains in the integrin headpiece through the RGD-containing module 10, but direct contact of the synergy-region-containing module 9 to integrin is not evident. This finding is corroborated by kinetic analysis of real-time binding data, which shows that the synergy site greatly enhances k(on) but has little effect on the stability or k(off) of the complex.

Amino Acid Substitution↗

PubMed2002

The role of the specificity-determining loop of the integrin beta subunit I-like domain in autonomous expression, association with the alpha subunit, and ligand binding.

Integrin beta subunits contain a highly conserved I-like domain that is known to be important for ligand binding. Unlike integrin I domains, the I-like domain requires integrin alpha and beta subunit association for optimal folding. Pactolus is a novel gene product that is highly homologous to integrin beta subunits but lacks associating alpha subunits [Chen, Y., Garrison, S., Weis, J. J., and Weis, J. H. (1998) J. Biol. Chem. 273, 8711-8718] and a approximately 30 amino acid segment corresponding to the specificity-determining loop (SDL) in the I-like domain. We find that the SDL is responsible for the defects in integrin beta subunit expression and folding in the absence of alpha subunits. When transfected in the absence of alpha subunits into cells, extracellular domains of mutant beta subunits lacking SDL, but not wild-type beta subunits, were well secreted and contained immunoreactive I-like domains. The purified recombinant soluble beta1 subunit with the SDL deletion showed an elongated shape in electron microscopy, consistent with its structure in alphabeta complexes. The SDL segment is not required for formation of alpha5beta1, alpha4beta1, alphaVbeta3, and alpha6beta4 heterodimers, but is essential for fomation of alpha6beta1, alphaVbeta1, and alphaLbeta2 heterodimers, suggesting that usage of subunit interface residues is variable among integrins. The beta1 SDL is required for ligand binding and for the formation of the epitope for the alpha5 monoclonal antibody 16 that maps to loop segments connecting blades 2 and 3 of beta-propeller domain of alpha5, but is not essential for nearby beta-propeller epitopes.

Amino Acid Sequence↗

PubMed2002

Quantitative analysis of adhesion molecules on cellular constituents of the human uterine microenvironment under the influence of estrogen and progesterone.

The uterus contains all the components of a tertiary lymphoid compartment. We hypothesize that specific leukocyte recruitment to the endometrium during the secretory phase of the menstrual cycle and early pregnancy limits the type of immunocyte that gains access. The present study utilized flow cytometry to define and quantify adhesion molecules possibly used by decidual infiltrating lymphocytes (DIL) as homing receptors, uterine microvascular myometrial endothelial cells (UtMVE-Myo) as addressins, and secretory endometrial stroma cells (STO) as retainment factors. Human umbilical cord vein endothelial cells and peripheral blood lymphocytes were used as control cells for comparison studies. DIL were composed of predominantly lymphocyte function-associated antigen (LFA)-1+, intercellular adhesion molecule (ICAM)-1+, LFA-2+, LFA-3+, gp150,95+, alpha1beta1+, Hermes cell adhesion molecule (H-CAM)+, and neural cell adhesion molecule (N-CAM)+ (CD56(bright)) memory/effector natural killer cells. A significant number of UtMVEC-Myo expressed platelet endothelial cell adhesion molecule (PECAM)-1, a percentage were uniquely LFA-3+, and alpha4 integrin expression was uniquely high. An increased number of STO uniquely expressed alpha3, beta3, and LFA-3, whereas alpha2, alpha4, alphaVbeta3, and H-CAM were significantly increased. Possible unique adhesions of DIL:UtMVEC-Myo included SLe(x):PECAM, vascular cell adhesion molecule-1:alpha4, and LFA-2:LFA-3, whereas DIL:STO included LFA-2:LFA-3 and N-CAM:N-CAM. Unique molecules on DIL may also associate with extracellular matrix (ECM) or complement on UtMVEC-Myo or STO to form gp150,95:fibrinogen/iC3b/C3dg, alpha1beta1:laminin (LM)/collagen (CO), and ICAM-1:fibronectin (FN) interactions. Bridges of ECM may also form between DIL and UtMVEC-Myo adhesion molecules including ICAM-1:FN:ICAM-1 and alpha4beta1:FN:alpha4beta1. DIL:ECM:STO interactions may involve alpha2beta1:CO:alpha2beta1, alpha3beta1:LM/CO/FN:alpha3beta1, alphaVbeta3:VN:alphaVbeta3, and H-CAM:hyaluronate:H-CAM. It is likely that many adhesion molecules play a role in the recruitment and retainment of specialized lymphocytes within the uterine microenvironment. (Mackay et al., 1990).

Adult↗

PubMed1998

Comparative analysis of integrins in vitro and in vivo in uveal and cutaneous melanomas.

Changes in integrin expression have been shown to be important for the growth and metastatic capacity of melanoma cells. In this study, we have examined the expression of alphav integrins by three uveal and four cutaneous malanoma lines. No lines expressed alphavbeta6 and only TXM13, a cutaneous line, expressed alphavbeta8. All lines expressed alphavbeta5 and alphavbeta3 (four out of four cutaneous, two out of three uveal) or avpl (OM431, an uveal line). Thus, OM431 is the second uveal melanoma we have described that expresses alphavbeta1 and this, we report again, functions as an alternative vitronectin/fibronectin receptor. Subcutaneous growth of cell lines in athymic mice correlated with an alphavbeta3-positive, alphavbeta1 -negative phenotype. Analysis of clinical material from cutaneous melanoma showed that although alphav expression was increased in 88% of metastases, this could not all be explained by up-regulation of alphavbeta3, with only 2 out of eight skin metastases expressing this heterodimer. Using antibody SZ.21, which as we report here works in archival material, only 1 out of 15 uveal metastases expressed detectable beta3. Thus, acquisition of alphavbeta3 expression, which has been implicated in cutaneous melanoma progression, may not be required for development of metastases from uveal melanoma or indeed for skin, as distinct from lymph node, metastases of cutaneous melanoma.

Animals↗

PubMed1997

A novel peptide motif for platelet fibrinogen receptor recognition.

To develop a specific antagonist of platelet alphaIIbbeta3 using small linear peptides, we synthesized a series of hexapeptides that did not have an Arg-Gly-Asp (RGD) sequence and examined their anti-platelet activity and their specificity for alphaIIbbeta3. We found a novel motif sequence, Pro-X1-X2-X3-Asp-X4, where X1 to X4 were all L-form alpha-amino acids, which specifically inhibited aggregation of human platelets at submicromolar concentrations. The Pro residue at the N terminus was essential to the anti-platelet activity, and the acetylation of the imino group of this residue also resulted in the complete loss of the activity. The results of the binding assay using purified human platelet alphaIIbbeta3 and placental alphavbeta3 and those of the cell adhesion assay suggest that this motif peptide is highly specific for platelet alphaIIbbeta3 among other integrins. Flow cytometric studies using an fluorescein isothiocyanate-labeled RGD peptide showed that this motif peptide inhibited the binding of an RGD peptide to activated platelets, suggesting that it has the same inhibitory mode as RGD peptides. Conformational analysis of this motif peptide and an RGD-containing peptide suggests that the imino group of the Pro residue may substitute for the role of the guanidino group of the Arg residue of the RGD sequence.

Animals↗

PubMed1998

Expression of alphav integrins and vitronectin receptor identity in breast cancer cells.

In the present study we have used fluorocytometry and immunoprecipitation to characterize the expression of alphav-containing integrins in a panel of eight human breast cancer cell lines and one normal human mammary epithelial line. We show that the classical vitronectin receptor alphavbeta3 is expressed in only one cell line (MDA-MB-231), whereas alphavbeta5 is expressed on all breast cancer cell lines and alphavbeta1 is expressed on the majority. Using adherence assays to purified ligands in the presence and absence of function-blocking monoclonal antibodies, we have demonstrated that alphavbeta5 mediates adhesion to vitronectin in the majority of these cells. In one cell line, ZR75-1, alphavbeta1 contributes significantly to adhesion to immobilized vitronectin. The formation of focal adhesions containing the alphav and beta1 subunits on vitronectin is also demonstrated by indirect immunofluorescence.

Breast Neoplasms↗

PubMed1998

L1 makes immunological progress by expanding its relations.

The cell-adhesion molecule L1 was originally described in the nervous system. It has recently been detected in CD4+ T lymphocytes, peripheral B lymphocytes, and granulocytes in the human immune system and in similar leucocyte types in the murine immune system. L1 mediates neural recognition by Ca+2, Mg+2-independent homophilic binding. In the human and murine immune systems, L1 binds to the "classical" vitronectin receptor, alphaVbeta3, and fibronectin receptor, alpha5beta1, respectively, and abstains from homophilic binding. Homophilic L1 binding probably involves antiparallel alignment of several interactive domains. Integrin binding is mediated by a short segment of immunoglobulinlike domain 6, which includes two RGD repeats in rodent L1 and one RGD motif in human L1. L1 is modulated in activated leucocytes in vitro in parallel to L-selectin, and diverse cell types release intact L1 in vivo and in vitro. Released L1 can bind to laminin and adheres to the extracellular matrix of sciatic nerve, M21 melanoma, and possibly spleen and other tissues. It can support integrin-dependent cell migration and preliminary data implicate it in tumor development and transnodal lymphocyte migration.

Amino Acid Sequence↗

PubMed2004

The mechanism of alphaIIbbeta3 antagonism by savignygrin and its implications for the evolution of anti-hemostatic strategies in soft ticks.

Savignygrin, a alphaIIbbeta3 antagonist presents the RGD sequence on the substrate-binding loop of the (BPTI-fold). This study investigated whether this is the only integrin-targeting motif associated with its mechanism. It forms a tight-binding complex with alphaIIbbeta3 that is resistant to SDS dissociation under reducing and non-reducing conditions, but not to temperature or EDTA. The same complex is formed on resting and activated platelets, as well as aggregated platelets that have been disaggregated with savignygrin. Binding of FITC labeled savignygrin to platelets show that the binding kinetics and affinity of savignygrin is similar for resting and activated platelets (Kd approximately 50-70 nM). Binding to resting or activated platelets was significantly inhibited by two savignygrin peptide fragments, S2 (GSRGDEDATFG) and S3 (FDREDGGSRQG) that correspond with two specific loop-like areas in the structure of savignygrin that together form a continuous binding interface. The inability of S3 to inhibit platelet aggregation indicates that it targets a novel ligand-binding site. A model of alphaIIbbeta3 based on the recent crystal structure of alphavbeta3 into which the RGD sequence of savignygrin was docked shows that savignygrin lies along the interface formed by the two subunits. A novel mode of integrin antagonism is indicated that includes the targeting of distinct sites on the alphaIIbbeta3 subunits. The S2 and S3 loops are not involved in the mechanisms of the related soft tick blood coagulation inhibitors and suggest that this allowed their evolution as integrin targeting motifs.

Amino Acid Sequence↗

PubMed1999

Previous uptake of apoptotic neutrophils or ligation of integrin receptors downmodulates the ability of macrophages to ingest apoptotic neutrophils.

Clearance of apoptotic neutrophils (polymorphonuclear leukocyte [PMN]) by macrophages is thought to play a crucial role in resolution of acute inflammation. There is increasing evidence that ingestion of apoptotic cells modulates macrophage behavior. We therefore performed experiments to determine whether ingestion of apoptotic PMN modulated the uptake process itself. Rat bone marrow-derived macrophages (BMDM) ingested apoptotic PMN by a process that was enhanced by tumor necrosis factor (TNF) and attenuated by interferon (IFN)-gamma, interleukin (IL)-4, and IL-10. It was inhibitable by the tetrapeptide arg-gly-gln-ser (RGDS), therefore implicating the alphavbeta3/CD36/thrombospondin pathway. Interaction of apoptotic PMN with BMDM for 30 minutes, 48 hours before rechallenge reduced uptake of apoptotic PMN by 50% compared with previously unchallenged BMDM. Blocking initial uptake with RGDS abrogated the effect of preexposure. Comparable and sustained attenuation of uptake was obtained by ligating alphavbeta3 with the monoclonal antibody (MoAb), F11, after a delay of more than 90 minutes, whereas MoAbs to CD25 and CD45 had no effect. Ligation of alpha6beta1 and alpha1beta2, integrins not previously implicated in the engulfment of apoptotic cells also decreased uptake with similar kinetics to F11. Therefore, apoptotic PMN regulate their own uptake through an integrin-dependent process, which can be reproduced by ligation of other integrins expressed by macrophages.

Animals↗

PubMed2006

Extracellular matrix regulates enhanced eotaxin expression in asthmatic airway smooth muscle cells.

RATIONALE: Altered airway smooth muscle (ASM) function and enrichment of the extracellular matrix (ECM) with fibronectin and collagen are key features of asthma. Previously, we have reported these ECM proteins enhance ASM synthetic function. OBJECTIVE: We compared ASM cultured from endobronchial biopsies from subjects with and without asthma to assess if asthmatic cells were hypersecretory and determined whether the underlying mechanism involved autocrine ECM production. METHODS AND MEASUREMENTS: Cells from subjects with and without asthma were cultured on plastic or in plates precoated with ECM proteins. Cytokine production was evaluated by enzyme-linked immunosorbent assay and by reverse transcriptase-polymerase chain reaction. Function-blocking integrin antibodies were used to identify integrin involvement. RESULTS: Baseline eotaxin and its production after stimulation with interleukin (IL)-13, IL-1beta, or tumor necrosis factor-alpha was increased (2.5- to 6.0-fold) in ASM cells cultured from subjects with asthma compared with healthy subjects. When seeded on ECM from asthmatic ASM, IL-13-dependent eotaxin release from healthy or asthmatic ASM was enhanced compared with culture on healthy ECM. The ECM substrates fibronectin and type I collagen each enhanced IL-13-dependent eotaxin release, and Western immunoblot indicated that fibronectin expression was higher in asthmatic ASM cells. Integrin-blocking antibodies revealed that alpha5beta1 was required for more than 50% of the enhanced IL-13-dependent eotaxin release by ASM cells from subjects with asthma, whereas alpha2beta1 or alphavbeta3 neutralization lacked effect. CONCLUSION: The data indicate that ASM cells cultured from subjects with asthma are hypersecretory compared with cells from healthy donors and that autocrine fibronectin secretion acting via alpha5beta1 in part underlies this effect.

Adult↗

PubMed2005

Differential pattern of integrin receptor expression in differentiated and anaplastic thyroid cancer cell lines.

Adhesion of tumor cells to the extracellular matrix (ECM) is a crucial step for the development of metastatic disease and is mediated by specific integrin receptor molecules (IRM). The pattern of metastatic spread differs substantially among the various histotypes of thyroid cancer (TC). However, IRM have only occasionally been characterized in TC until now. IRM expression was investigated in 10 differentiated (FTC133, 236, 238, HTC, HTC TSHr, XTC, PTC4.0/4.2, TPC1, Kat5) and two anaplastic TC cell lines (ATC, C643, Hth74), primary cultures of normal thyroid tissue (Thy1,3), and thyroid cancer specimens (TCS). Expression of 16 IRM (beta1-4, beta7, alpha1-6, alphaV, alphaIIb, alphaL, alphaM, alphaX) and of four IRM heterodimers (alpha2beta1, alpha5beta1, alphaVbeta3, alphaVbeta5), was analyzed by fluorescent-activated cell sorter (FACS) and immunohistochemical staining. Thyroid tumor cell adhesion to ECM proteins and their IRM expression in response to thyrotropin (TSH) was assessed. Follicular TC cell lines presented high levels of integrins alpha2, alpha3, alpha5, beta1, beta3 and low levels of alpha1, whereas papillary lines expressed a heterogenous pattern of IRM, dominated by alpha5 and beta1. ATC mainly displayed integrins alpha2, alpha3, alpha5, alpha6, beta1 and low levels of alpha1, alpha4 and alphaV. Integrin heterodimers correlated with monomer expression. Evaluation of TCS largely confirmed these results with few exceptions, namely alpha4, alpha6, and beta3. The ability of TC cell lines to adhere to purified ECM proteins correlated with IRM expression. TSH induced TC cell adhesion in a dose-dependent fashion, despite an unchanged array of IRM expression or level of a particular IRM. Thyroid carcinoma cell lines of different histogenetic background display profoundly different patterns of IRM expression that appear to correlate with tumor aggressiveness. In vitro adhesion to ECM proteins and IRM expression concur. Finally, TSH-stimulated adhesion of thyroid tumor cell lines to ECM may not be associated with altered IRM expression.

Carcinoma↗

PubMed1999

A mutation in the alpha subunit of the platelet integrin alphaIIbbeta3 identifies a novel region important for ligand binding.

An unbiased genetic approach was used to identify a specific amino acid residue in the alphaIIb subunit important for the ligand binding function of the integrin alphaIIbbeta. Chemically mutagenized cells were selected by flow cytometry based on their inability to bind the ligand mimetic antibody PAC1 and a cell line containing a single amino acid substitution in alphaIIb at position 224 (D-->V) was identified. Although well expressed on the surface of transfected cells, alphaIIbD224Vbeta3 as well as alphaIIbD224Abeta3 did not bind alphaIIbbeta3-specific ligands or a RGD peptide, a ligand shared in common with alphavbeta3. Insertion of exon 5 of alphaIIb, residues G193-W235, into the backbone of the alphav subunit did not enable the chimeric receptor to bind alphaIIbbeta3-specific ligands. However, the chimeric receptor was still capable of binding to a RGD affinity matrix. alphaIIbD224 is not well conserved among other integrin alpha subunits and is located in a region of significant variability. In addition, amino acid D224 lies within a predicted loop of the recently proposed beta-propeller model for integrin alpha subunits and is adjacent to a loop containing amino acid residues previously implicated in receptor function. These data support a role for this region in ligand binding function of the alphaIIbbeta3 receptor.

Amino Acid Sequence↗

PubMed2001

Distribution of cytoskeletal proteins, integrins, leukocyte adhesion molecules and extracellular matrix proteins in plastic-embedded human and rat kidneys.

OBJECTIVE: To study the distribution of cytoskeletal proteins (actin, alpha-actinin, vinculin, beta-tubulin, keratin, vimentin, desmin), adhesion molecules for cell-matrix interations (very later antigens [VLA1-61, beta1, beta2 [CD18], vitronectin receptor [alphavbeta3], CD 11b), leukocyte adhesion molecules (ICAM-1) and extracellular matrix proteins (collagen IV, fibronectin, laminin, vitronectin) in human and rat kidneys by using a superior processing and immunohistochemical staining technique. STUDY DESIGN: Human and rat kidneys were fixed in 2% paraformaldehyde, dehydrated in acetone and processed in a new, low-toxic glycol, methacrylate mixture, especially developed for immunohistochemistry. Both the glomeruli and the interstitial areas were carefully examined and scored semiquantitatively. RESULTS: Immunostained plastic sections showed excellent morphology combined with remarkably well preserved antigenicity. CONCLUSION: The above mentioned provides an excellent tool for the accurate localization of a wide variety of antigens at the light microscopic level.

Animals↗